The invention relates to a method for production monitoring with the manufacture of tablets in a rotary tabletting machine.
From EP 0 431 2689 it is known with the manufacture of tablets to continuously measure the applied pressing forces and to compare these with nominal values. If a measured maximum pressing force value lies outside nominal value limits the tablet concerned is sorted out. Each punch pair of the rotary press has an order number so that with a deviation from the nominal value it is certain which punch pair or matrix bore is concerned. With the help of such a method the quality of the tablets may be continuously monitored.
From the mentioned document it is also known by way of the application of an angular impulse outputter to evaluate the respective position of the matrix disk and to coordinate this with the maximum pressing force values. By way of this a monitoring may also be continued with an exchange of a matrix disk without an adjustment of the electronic means being required.
From EP 0 350 563 it is also known, from the measuring results for the maximum pressing forces, to form a mean value and to compare this with tolerance limits. The course of the pressing force values gives conclusions as to the degree of filling of the matrix bores. If the mean value exceeds the tolerance limits a readjustment of the filling of the matrix bores is carried out. In this way a control may be effected relatively quickly. For evaluation of the mean values a few rotations of the press rotor are sufficient, by which means a useable mean value is available within a few seconds. The control of the filling may therefore likewise be effected in the shortest of times. Errors which occur on account of an unexact degree of filling may therefore be alleviated relatively quickly.
From EP 0 350 563 it is also known to set tolerance limits for the pressing forces of each individual punch pair. If the tolerance limits are exceeded this is a sign for an inadequate functioning of this punch pair, for example on account of a fracture, the adhesion of material, of the bursting away of the pressing surface on the punch head and likewise.
For maintaining quality, it is finally known from time to time, for example in an interval of quarter of an hour, to take samples. A row of tablets, for example 20, are removed from the production. From the weight of the tablets a mean value is formed which is compared to a nominal mean value. If the measured mean value deviates from predetermined tolerance limits, the supply of material to be pressed is readjusted.
With the evaluation of mean values for the pressing force adulterations may occur which displace the mean value by a measure which does not correspond to actual ratios. Thus on account of an error in the data transmission an erroneous reading may be transmitted to the computer. This error may occur temporarily or permanently. Furthermore by way of damage to a punch pair or the adhesing of material or by way of irregular supply of material a pressing force value may arise which deviates significantly from the remaining pressing force values of a measuring row. The described errors or disturbances lead to a mean value and thus to a readjustment for the material filling which are not justified by the other pressing force values. As a result such a filling degree control causes undesired fluctuations in the tablet weight.